Magnetic steering wheel movement sensing device

ABSTRACT

A steering wheel movement detection device has a magnetic flux source and a magnetic sensor. The magnetic sensor is mounted on the steering column and the magnetic flux source is attached to the steering shaft or steering wheel and moves in accordance therewith. The magnetic flux source has lines or bands of varying magnetic flux. The magnetic sensing device is mounted adjacent and opposing the magnetic flux source so that when the steering wheel moves varying magnetic flux impinges upon the magnetic sensing device. The magnetic sensing device forms the inductive component of a resonant LC tank circuit and the frequency of that circuit varies in accordance with the flux impinging on the sensing device. A microcontroller integrates or averages the varying frequency signal over brief periods of time and when the average frequency does not have sufficient deviations an alarm signal is produced. A speaker is driven by the alarm signal to signal the driver to a state of alertness. A cruise control deactivation signal is also produced by the apparatus to disengage cruise control mode when driver alertness is in question.

This invention claims the benefit of provisional application No.60/078,455, filed Mar. 18, 1998.

FIELD OF THE INVENTION

This invention is in the field of vehicle steering and speed sensitivedevices to detect a lack of driver alertness and emit a warningthereupon.

BACKGROUND OF THE INVENTION

Numerous systems are known that sense vehicle steering correctionsduring a given time period as an indication of driver alertness. Onesuch system is disclosed in U.S. Pat. No. 4,278,969 to Richard Woods,entitled “Driver Warning System”. The '969 Woods device incorporates alight source and photocell mounted on the steering column that directs alight beam towards a strip having alternate bands of reflective andnon-reflective material. During normal driving patterns, the steeringwheel is corrected a given number of times during any predetermined timeperiod. When steering corrections fall below the predetermined number,the driver is usually inattentive due to any of a number of reasons. Anaudible driver warning system during such conditions has been shown tobe effective to arouse the driver to a state of alertness to prevent avehicle accident. For example, the Woods system is coupled with vehiclespeed sensing devices which make it inoperative below a certain vehiclespeed so that when the vehicle is parked or moving at a relatively slowspeed, the audible alarm will not be sounded even though the necessarysteering corrections are not made within the given time period. Onesignificant shortcoming of the Woods device is its reliance on opticsfor motion detection.

Optical devices used in a motor vehicle environment are subject tosignificant amounts of dirt, grime, grease and other likelycontaminants. Such contaminants will likely interfere with and preventthe Woods device from functioning properly. A steering wheel movementdetection device that is unaffected by such contaminants is needed.

SUMMARY OF THE INVENTION

A steering wheel movement sensing apparatus for use with a vehiclehaving a steering shaft, according to one aspect of the presentinvention, comprises magnetic sensing means for detecting variations inmagnetic flux, the magnetic sensing means attached at a fixed locationwithin the vehicle in close proximity to the steering shaft, themagnetic sensing means producing a magnetic signal in accordance withthe magnetic flux impinging thereon, a magnetic strip having varyingmagnetic flux lines, the magnetic strip attached to the steering shaftand in close proximity to the magnetic sensing means so that magneticflux emanating from the magnetic strip impinge upon the magnetic sensingmeans, and wherein the magnetic strip moves with respect to the magneticsensing means when the steering shaft is rotated, circuit meansresponsive to the magnetic signal for producing an alarm signal inaccordance with a lack of deviation in the magnetic signal, and alarmmeans responsive to the alarm signal for producing an audible sound inaccordance with the alarm signal.

One object of the present invention is to provide an improved steeringwheel movement detection device.

Another object of the present invention is to provide steering wheelmovement detection device that is unaffected by contaminants normallyencountered in a motor vehicle environment.

Yet another object of the present invention is to provide a morereliable and more economical steering wheel movement detection device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a steering wheel movement sensing deviceaccording to one aspect of the present invention.

FIG. 2 is a block diagram of another embodiment of a steering wheelmovement sensing device according to another aspect of the presentinvention.

FIG. 3 is an electrical circuit schematic for the embodiments shown inFIGS. 1 and 2.

FIG. 4 is a flowchart for the program executed by microcontroller 24 ofFIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIG. 1, a block diagram of a magnetic steering wheelmovement sensing device 10 according to the present invention is shown.Device 10 includes a magnetic strip 12, a magnetic sensor 14, a sensorcircuit 16, a mode switch 18, a mode indicator or lamp 20, a powerindicator or lamp 22, a microcontroller 24, a speaker 26, a power supplyregulator 28 and a power switch 30. Magnetic strip 12 includes aplurality of magnetized areas 13 that produce a plurality of magneticlines of flux emanating from strip 12. Magnetic sensor 14 includes abobbin 15 about which a coil 17 is wound. Additionally, a magnet 19 ismechanically attached to bobbin 15 as shown. Bobbin 15 is made offerrite or other known magnetic materials. Conductors 17a are the twoleads from coil 17. Conductors 17a are connected to sensor circuit 16.Circuit 16 is shown in more detail in FIG. 3. Circuit 16 includes anoscillator circuit wherein the coil 17 provides the inductive componentof the LC oscillator circuit. As magnetic strip 12 is moved with respectto sensor 14, the inductance of coil 17 is altered accordingly. Thus,the oscillator circuit of sensor circuit 16 will vary in frequencycorrespondingly with the magnetic flux lines from magnetic strip 12 thatimpinge upon sensor 14.

Sensor circuit 16 supplies an oscillator signal microcontroller 24.Microcontroller 24 monitors the frequency signal from circuit 16 andproduces an alarm signal supplied to speaker 26 when the deviation infrequency in the signal from circuit 16 fails to exceed a predetermineddeviation over a predetermined time period. Mode switch 18 provides aninput signal to microcontroller 24 so that microcontroller 24 issignaled or instructed to enter into an alternative mode of operation.Alternative modes of operation are useful during the installationprocess of device 10 into a motor vehicle. Mode light 20 receives anactivation signal from microcontroller 24 to indicate the current modeof operation of the microcontroller. Switch 30 provides a mechanism toswitch on and off the power supplied by an external DC power source (notshown). Power supply regulator 28 produces a regulated DC output signalused by microcontroller 24 and sensor circuit 16. Power lamp 22 receivesa power signal from regulator 28. Power lamp 22 provides a visualindication that power is supplied to device 10.

Operationally speaking, magnetic strip 12 is attached to the steeringshaft or steering wheel of a motor vehicle. Magnetic sens or 14 ismounted in a fixed position adjacent and in close proximity to magneticstrip 12. As the steering wheel or steering shaft is rotated, strip 12is moved with respect to sensor 14 thereby causing a variation in theinductance of coil 17. Sensor circuit 16, which include an LC oscillatorcircuit (FIG. 3) or tank circuit produces an oscillator signal that issupplied to microcontroller 24. As magnetic strip 12 moves versus thestationary sensor 14, the frequency of t he signal produced by thecircuit 16 varies in accordance with the flux impinging on the sensorfrom strip 12. Under normal driving conditions, microcontroller 24monitors the oscillator signal from circuit 16 in a continuous fashion.Preferably, the period of the oscillator signal is averaged over a fixedperiod of time to determine a current frequency. Then, the period of theoscillator signal is averaged again over a second interval of time (forexample 25-200 milliseconds), and compared with the previous average toascertain whether sufficient deviation is detected. If the frequencydeviation fails to exceed a predetermined deviation quantity over athree to five second period, then microcontroller 24 will produce analarm signal supplied to speaker 26. Finally, a cruise control disablesignal 32 is produced by microcontroller 24 when the alarm signalsupplied to speaker 26 is produced. Signal 32 is connected to a cruisecontrol device (not shown) to deactivate the cruise control device from“cruise” mode and begin deceleration of the vehicle when the lack ofsteering wheel movement indicates the driver may not be alert.

Referring now to FIG. 2, another embodiment of a steering wheel movementsensing device 40 according to the present invention is shown. All ofthe components shown in FIG. 2 are identical with those shown in FIG. 1with the exception of the toothed wheel 32. Wheel 32 takes the place ofmagnetic strip 12 in device 40. All components of FIG. 2 that are likenumbered in FIG. 1 have the same characteristics and functionality asthose device described with respect to device 10 of FIG. 1. The toothedwheel 32 provides an inductive interaction with sensor 14 so that smallvariations in the inductance of coil 17 are present on the leads 17 afrom coil 17. Leads 17 a are connected into an LC tank circuit in sensorcircuit 16. Toothed wheel 32 is mounted on or attached to the steeringwheel or steering shaft of a motor vehicle and rotates in accordancewith the steering shaft. In all other aspects of operation, device 40 isidentical in functionality and components with device 10.

Referring now to FIG. 3, a schematic diagram of an electrical circuitused with the steering wheel movement sensing devices 10 and 40 isshown. Inductor L1 corresponds to coil 17 of FIGS. 1 and 2. Sensorcircuit 16 is indicated by a broken line and includes an oscillatorcircuit 50 and a common emitter amplifier circuit 52. The oscillatorcircuit 50 is a traditional Colpitts oscillator well known in the art ofelectronics, and further discussion thereof is not necessary herein.Capacitor C1 and C2 and inductor L1 provide the LC components of theoscillator circuit 50. Resistors R1, R2 and R3 provide DC bias voltagesto transistor Q1. The oscillator signal from circuit 50 passes throughdecoupling capacitor C3 and into the common emitter amplifier circuit 52comprised of resistors R4, R5, R6 and R7 and transistor Q2. ResistorsR4-R7 provide the DC bias voltages for amplifier transistor Q2.Amplifier circuit 52 is a high gain amplifier and transforms theoscillator signal delivered to the base of Q2 into a square wave signal.

The output of sensor circuit 16 is an approximately seven kilohertzfrequency signal that is supplied to an input of microcontroller 24indicated in FIG. 3 as U1. Microcontroller U1 received an input signalfrom switch S1 that corresponds with the mode switch 18 in FIGS. 1 and2. LED D1 corresponds to the mode light 20 in FIGS. 1 and 2. LED D1 isilluminated or activated when microcontroller U1 detects insufficientfrequency deviation in the oscillator signal from sensor circuit 16 inthe aforementioned three-five second time period. Speaker 26 correspondsto the device labeled “beeper1” in FIG. 3. Microcontroller 24 providestwo different output signals to jumper block JP1, and depending on thebrand of speaker or beeper used, a short is installed between pins 1 and2 of JP1 or between pins 2 and 3 of JP1. Crystal Y1 and capacitors C6and C7 provide an oscillator signal to microcontroller U1. U2 is a 5volt regulator device well known in the electronics art for reducing ahigher DC voltage such as that produced by a motor vehicle (+12 VDC) tothe five volts DC required by microcontroller U1.

Referring now to FIG. 4, a flowchart of the computer program executed bymicrocontroller 24 is shown. The flowchart begins at step 60. Next, atstep 62, the input and output ports of the microcontroller areinitialized to a predetermined desired state. At step 64, internaltimers of the microcontroller are loaded with values so that a 50millisecond and a 250 millisecond timer signal are produced. Next, atstep 66, several registers or program variables are initialized. Theseinclude measured frequency registers, FREQ_COUNT variable, FREQ_TOTALvariable, FREQ_TOTAL variable, and a FREQ_TOTAL_NEW variable. Timer andfrequency inputs interrupts are intialized next at step 68. At steps 70and 72 program operational features are activated in accordance with theground/floating state of the signals labeled TIME1, TIME2, TIME3, TIME4,CADE and SENS shown in the schematic of FIG. 3. For example, the TIME1,TIME2 and TIME3 inputs provide a 3-bit binary input to microcontroller24 to establish 1 of 8 possible alarm duration periods (such as 1-8seconds) that the alarm signal will be produced when the frequencydeviation of the signal from sensor circuit 16 is less than apredetermined deviation limit (as determined by microcontroller 24). TheCADE signal instructs the microcontroller 24 to produce either acontinuous alarm signal or an intermittent alarm signal based upon theground/floating state thereof. Finally, the sensitivity of sensorcircuit 16 may vary from installation to installation (the minimum andmaximum frequency produced by circuit 16) and the SENS signal instructsmicrocontroller 24 to establish a smaller or larger frequency deviationlimit when testing the frequency of the signal from circuit 16.

The microcontroller program control loop begins at step 74. At step 76,the frequency signal from circuit 16 is detected and averaged over a 50millisecond time period. Then, at step 78, the current frequency averageis compared with the previously computed frequency average, and if thedifference is greater than a predetermined value, program executioncontinues at step 80 and the alarm timer is reset. After step 80,program execution continues at step 74. If the comparison at step 78results in a deviation in frequency that is less than the limit, thenprogram execution will continue to step 82.

At step 82, the alarm timer is tested to ascertain whether it hasexpired. If so, then the program continues at step 84 where the state ofthe “armed flag” is checked. If the armed flag is active, then programexecution continues at step 86. At step 86 the alarm is activated. Next,at step 88, the microcontroller pauses for one second. Then, at step 90,the microcontroller activates the external alarm output signal causingan alarm signal supplied to speaker 26. Program execution continues atstep 74 following step 90.

If at step 82 the alarm timer has not expired, then program executionwill continue with step 92. At step 92, microcontroller 24 detectswhether switch S1 is pressed. Recall that switch S1 in the FIG. 3schematic corresponds to the mode switch 18 in FIGS. 1 and 2. If at step92 the switch is detected as pressed, then step 94 is executed and thetoggle armed flag step is performed. Program execution continues at step74 following step 94.

If the button is not pressed at step 92, then program executioncontinues at step 98. If at step 98 it is determined that the button hasbeen pressed for more than three seconds, then step 96 is executed andthe test mode operation of device 10 is toggled on or off, oractivated/deactivated. Test mode causes microcontroller 24 to produce afeedback alarm signal useful in establishing the appropriate distancewhen installing the magnetic strip 12 and magnetic sensor 14 into amotor vehicle. Test mode provides continuous feedback in the form ofaudible short beeps from speaker 26 indicating to the installer thatfrequency deviations in the signal from sensor circuit 16 are beingsensed by microcontroller 24. Following step 96 program executionreturns to step 74.

If at step 98 the button has not been impressed for more than threeseconds then step 100 is executed and the alarm time is set to the valueon jumpers TIME1, TIME2 and TIME3.

While the invention has been illustrated and described in detail in thedrawings and foregoing description of the preferred embodiment, the sameis to be considered as illustrative and not restrictive in character, itbeing understood that only the preferred embodiment has been shown anddescribed and that all changes and modifications that come within thespirit of the invention are desired to be protected.

What is claimed is:
 1. A steering wheel movement sensing apparatus foruse with a vehicle having a steering shaft, said apparatus comprising:magnetic sensing means for detecting variations in magnetic flux, saidmagnetic sensing means attached at a fixed location within the vehiclein close proximity to said steering shaft, said magnetic sensing meansproducing a magnetic signal in accordance with the magnetic fluximpinging thereon, and wherein said magnetic sensing means includes anLC oscillator circuit, a coil wherein said coil is the inductivecomponent in said LC oscillator circuit, and wherein said magneticsignal is the frequency of said LC oscillator circuit that varies infrequency in accordance with the magnetic flux from said magnetic stripimpinging on said coil; a magnetic strip having varying magnetic fluxlines, said magnetic strip attached to said steering shaft and in closeproximity to said magnetic sensing means so that magnetic flux emanatingfrom said magnetic strip impinge upon said magnetic sensing means, andwherein said magnetic strip moves with respect to said magnetic sensingmeans when the steering shaft is rotated; circuit means responsive tosaid magnetic signal for producing an alarm signal in accordance with alack of deviation in said magnetic signal; and alarm means responsive tosaid alarm signal for producing an audible sound in accordance with saidalarm signal.
 2. The apparatus of claim 1 including a core disposedwithin said coil and a magnet disposed adjacent said core, and whereinsaid core is disposed between said magnetic strip and said magnet inclose proximity to said magnetic strip and in contact with said magnet.3. The apparatus of claim 2 wherein said core is cylindrical and madefrom ferrite material.
 4. The apparatus of claim 3 wherein said circuitmeans includes: a) timer means for producing a periodic timer signal;and b) frequency deviation detection means for detecting the magnitudeof deviations in the frequency of said LC oscillator circuit andproducing a frequency deviation signal corresponding to deviations inthe frequency of said oscillator circuit; and c) alarm circuit meansresponsive to said periodic timer signal and said frequency deviationsignal, said alarm circuit means producing said alarm signal when saidfrequency deviation signal is less than a predetermined deviation limitfor a time period in excess of the period of said periodic timer signal.5. The apparatus of claim 4 including a mode switch and wherein saidalarm circuit is connected to and responsive to said mode switch tocease producing said alarm signal when said mode switch is momentarilyactivated.
 6. The apparatus of claim 5 wherein said alarm signal issupplied to a cruise control device to deactivate the cruise mode of thecruise control device.
 7. The apparatus of claim 6 wherein said timermeans, said frequency deviation detection means and said alarm circuitmeans are portions of a single chip microcontroller.
 8. A steering wheelmovement sensing apparatus for use with a vehicle having a steeringshaft, said apparatus comprising: magnetic sensing means for detectingvariations in magnetic flux, said magnetic sensing means attached at afixed location within the vehicle in close proximity to said steeringshaft, said magnetic sensing means producing a magnetic signal inaccordance with the magnetic flux impinging thereon, wherein saidmagnetic sensing means includes an LC oscillator circuit, a coil whereinsaid coil is the inductive component in said LC oscillator circuit, andwherein said magnetic signal is the frequency of said LC oscillatorcircuit that varies in frequency in accordance with the magnetic fluxfrom said magnetic strip impinging on said coil; ferro-magnetic meansattached to said steering shaft and in close proximity to said magneticsensing means, wherein said ferro-magnetic means is a metallic memberhaving a plurality of raised spaced-apart protrusions and wherein saidferro-magnetic moves with respect to said magnetic sensing means whenthe steering shaft is rotated; circuit means responsive to said magneticsignal for producing an alarm signal in accordance with a lack ofdeviation in said magnetic signal; and alarm means responsive to saidalarm signal for producing an audible sound in accordance with saidalarm signal.
 9. The device of claim 8 including a core disposed withinsaid coil and a magnet disposed adjacent said core, and wherein saidcore is disposed between said magnetic strip and said magnet in closeproximity to said magnetic strip and in contact with said magnet. 10.The device of claim 9 wherein said circuit means includes: a) timermeans for producing a periodic timer signal; and b) frequency deviationdetection means for detecting the magnitude of deviations in thefrequency of said LC oscillator circuit and producing a frequencydeviation signal corresponding to deviations in the frequency of saidoscillator circuit; and c) alarm circuit means responsive to saidperiodic timer signal and said frequency deviation signal, said alarmcircuit means producing said alarm signal when said frequency deviationsignal is less than a predetermined deviation limit for a time period inexcess of the period of said periodic timer signal.
 11. A steering wheelmovement sensing apparatus for use with a vehicle having a steeringshaft, said apparatus comprising: magnetic sensing means for detectingvariations in magnetic flux, said magnetic sensing means attached at afixed location within the vehicle in close proximity to said steeringshaft, said magnetic sensing means producing a magnetic signal inaccordance with the magnetic flux impinging thereon, wherein saidmagnetic sensing means includes an LC oscillator circuits, a coilwherein said coil is the inductive component in said LC oscillatorcircuit, and wherein said magnetic signal is the frequency of said LCoscillator circuit that varies in frequency in accordance with themagnetic flux from said magnetic strip impinging on said coil;ferro-magnetic means attached to said steering shaft and in closeproximity to said magnetic sensing means, wherein said ferro-magneticmoves with respect to said magnetic sensing means when the steeringshaft is rotated, and wherein said ferro-magnnetic means is a magneticstrip having varying magnetic flux lines; circuit means responsive tosaid magnetic signal for producing an alarm signal in accordance with alack of deviation in said magnetic signal; and alarm means responsive tosaid alarm signal for producing an audible sound in accordance with saidalarm signal.
 12. The device of claim 11 including a core disposedwithin said coil and a magnet disposed adjacent said core, and whereinsaid core is disposed between said magnetic strip and said magnet inclose proximity to said magnetic strip and in contact with said magnet.13. The device of claim 12 wherein said circuit means includes: a) timermeans for producing a periodic timer signal; and b) frequency deviationdetection means for detecting the magnitude of deviations in thefrequency of said LC oscillator circuit and producing a frequencydeviation signal corresponding to deviations in the frequency of saidoscillator circuit; and c) alarm circuit means responsive to saidperiodic timer signal and said frequency deviation signal, said alarmcircuit means producing said alarm signal when said frequency deviationsignal, is less than a predetermined deviation limit for a time periodin excess of the period of said periodic timer signal.
 14. The device ofclaim 13 wherein said timer means, said frequency deviation detectionmeans and said alarm circuit means are portions of a single chipmicrocontroller.